Method of adjusting phase shift in amplification multicavity klystron and device therefor

ABSTRACT

A method of adjusting a phase shift in an amplification multicavity klystron comprises the steps of tapping a portion of signal from output and intermediate resonators of a klystron, adding up the tapped signals, adjusting the amplitudes and phases of the tapped signals so that said signals have equal amplitude but opposite phases with the klystron operating under nominal conditions and applying the sum signal to an input resonator whereupon anode voltage is varied until a phase shift in the klystron changes, the subsequent step being the selection of the phase of the sum signal to provide for a minimum phase-shift variation in the klystron. A device for executing the proposed method of adjusting a phase shift includes a line composed of a phase shifter, an adder, and an additional phase shifter. One input of the phase shifter is connected to the output resonator of the klystron, while the other input thereof is coupled to the adder. The additional phase shifter is connected to the input resonator of the klystron and to the adder, whereas the adder is coupled to the phase shifters and to the intermediate resonator of the klystron.

FIELD OF THE INVENTION

The present invention relates to electronic engineering and inparticular to a method of adjusting a phase shift in an amplificationmulticavity klystron and a device therefor.

PRIOR ART

At the present time a phase shift of O-type amplifiers is normallystabilized by regulating power sources, particularly anode voltagesources which influence the phase shift value more markedly. So, forexample, a 1% variation of anode voltage causes the phase shift of anoutput signal to change by tens of degrees in travelling-wave tubes andby ten or more degrees in a klystron, depending on the operatingfrequency band and mu factor. In stabilizing the phase shift byregulating power sources, an anode voltage stability of about 10⁻⁴ isrequired to obtain a phase-shift stability of some 0.1° in modernradars. Considerable difficulties are encountered in providing suchstability of anode voltage, particularly in pulsed operation withdevices having a variable on-off ratio, a disadvantage generallyresulting in increased dimensions and weight of an anode voltage source.

Known in the art are methods of enhancing stability of a phase shift inO-type devices, which permit obtaining desired stability with mediumanode voltage regulation levels.

Another known method involves correction of phase differences intravelling-wave tubes operating in parallel (cf. U.S. Pat. No.3,958,184, Cl.328-155, 1976). The aforesaid method comprises the stepsof tapping a portion of an output signal from an amplifier, comparingthe output signal with a signal derived from a reference system,obtaining voltage proportional to a difference in phases of the signalsbeing compared, and utilizing said voltage for controlling aphase-shifter located ahead of the input of a travelling-wave tube. Theaforesaid method has been generally unsatisfactory due to low responseattributed to the operation of an a-f feedback circuit and its intricatestructure, a factor substantially limiting the field of itsapplications.

The prototype of the hereinproposed method of adjusting a phase shift ina klystron is a known method employing negative feedback between theoutput and input of a klystron (cf. "Automatic Phase Incursion Controlin Amplifiers" edited by M. V. Kapranov, "Soviet Radio" publishers,Moscow, 1972), wherein a portion of the output signal power is fed tothe input of the klystron in antiphase with the input signal. Theoperating speed provided by such a method equals several r-f oscillationperiods, a value high enough as compared with the rise time of signalsin radio sets. Another advantage of the foregoing method is acomparatively simple feedback circuit.

However, the process of enhancing phase-shift stability in the device isaccompanied by corresponding decreases in the mu factor, a disadvantageassociated with the fact that the feedback signal voltage is subtractedfrom the input signal voltage. The fuller the compensation of phaseinstability of the device, the higher will be the losses in the mufactor.

The known device for accomplishing the aforesaid method of adjusting aphase shift by employing negative feedback between the output and inputof a klystron comprises a line for transmitting a signal from an outputresonator to an input resonator of said klystron, a phase shifter foradjusting the phase of a signal applied to the input resonator and, ifrequired, a filter for preventing self-oscillations at frequenciescorresponding to positive feedback.

DISCLOSURE OF THE INVENTION

The invention resides in providing a method of adjusting a phase shiftin an amplification multicavity klystron and a device therefor, whichmake it possible to prevent any change in a phase shift in a klystron inthe case of anode voltage variations as small as a few percent withoutlosses in the mu factor. The method is accomplished by employing twofeedback channels.

The foregoing object is attained by providing a method of adjusting aphase shift in an amplification multicavity klystron involving thetapping of a portion of a signal from an output resonator, whereinaccording to the invention, the following additional steps are carriedout tapping a portion of signal from an intermediate resonator, addingup the signals tapped from the output and intermediate resonators,applying the sum signal to an input resonator of the klystron, andadjusting the amplitudes and phases of the tapped signals so that thetapped signals have equal amplitudes but opposite phases, whereuponanode voltage is varied until the phase shift in the klystron changes,the subsequent step being the selection of the phase of the sum signalso as to provide a minimum phase-shift variation in the klystron.

Since with operating anode voltage a signal fed to the input resonatorfrom the adder is zero, the input power and mu factor of the klystronwill be essentially the same as in a device having no feedback circuits.The phase-shift compensation level with a slight variation of theoperating voltage depends on the values of signals tapped from theoutput and intermediate resonators. The signal value corresponding tofull phase-shift compensation is determined by the ratio betweendistances from the intermediate resonator to the input and outputresonators. With a smaller value of the tapped signals it is possible topartially adjust the phase shift, while a greater value of the tappedsignals enables the phase shift opposite to the phase shift in klystronshaving no feedback circuits.

The foregoing object is also accomplished by providing that, in a devicefor executing the proposed method, a phase shift in an amplificationmulticavity klystron is provided, and the device includes a line fortransmitting a signal from an output resonator to an input resonator ofsaid klystron through a phase shifter, and, according to the invention,said line incorporates a signal adder coupled to the intermediate andinput resonators, while an additional phase shifter is inserted betweenthe adder and the input resonator to provide for selection of the phaseof an adjusting signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further with reference to specificembodiments thereof, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 depicts a device for executing a method of adjusting a phaseshift in an amplification multicavity klystron according to theinvention;

FIG. 2 is a vector diagram illustrating r-f voltages in an inputresonator with anode voltage corresponding to nominal operatingconditions of a klystron according to the invention; and

FIG. 3 is a vector diagram illustrating r-f voltages in an inputresonator with varying anode voltage.

PREFERRED EMBODIMENT OF THE INVENTION

Referring to the drawings the device for adjusting a phase shift in anamplification klystron 1 (FIG. 1), comprises an input resonator 2, anintermediate resonator 3, an output resonator 4, a line composed of aphase shifter 5 whose output is connected to one input of an adder 6,and an additional phase shifter 7 connected to a second input to theadder. The input of the phase shifter 5 is coupled to the outputresonator 4, whereas the additional phase shifter 7 is connected to theinput resonator 2 of the klystron 1. A third input of the adder 6 isconnected to the intermediate resonator 3, while a fourth input thereofis coupled through a detector 8 to an indicator 9 indicating the signallevel in the adder 6. Besides, a phase meter 10 is placed between theinput and output resonators 2 and 4 of the klystron 1 during analignment procedure.

It is essential that one of the coupling elements feeding a portion ofpower from the output resonator 4 and from the intermediate resonator 3of the klystron 1 to the adder 6, say, the element for coupling with theoutput resonator 4, should be adjustable as regards a transmitted powerlevel. The adjustment may also be accomplished by placing a variableattenuator ahead of the adder 6. The adder 6 may represent a T-elementwith an additional lead for the signal level indicator 9 or a cavityresonator having four leads. If the adder 6 is a T-element, a cavityresonator or a narrowband filter with two leads may be placed in theline between the adder 6 and the input resonator 2 of the klystron 1.The indicator 9 indicating the signal level in the adder may also bemounted at any point of the line. Decoupling elements may be inserted inthe line to prevent the reflection effect.

The device may be aligned by the following method:

disconnecting a coupling element 11 if no decoupling element is placedin the line between the adder 6 and the input resonator 2 of theklystron 1;

adjusting alternately the coupling with the output resonator 4 and thephase shifter 5 so that the signals in the adder 6 fed from the outputand intermediate resonators 4 and 3 have equal amplitudes but oppositephases (in this case, the r-f signal in the adder 6 is zero and theindicator 9 signalling signal level in the adder 6 reads zero);

connecting the additional phase shifter 7 to the input resonator 2;

measuring the phase shift in the klystron 1 with the phase meter 9 undernominal operating conditions; and

varying anode voltage and adjusting the additional phase shifter 7 so asto provide a minimum phase-shift variation in the klystron 1.

The method of adjusting a phase shift in the amplification multicavityklystron 1 involving the tapping of a portion of signal from the outputresonator 4 comprises the additional steps of tapping a portion of thesignal from the intermediate resonator 3, adding up the signals from theoutput and intermediate resonators 4 and 3, adjusting the phase andamplitude of one of the tapped signals, say, the phase and amplitude ofthe signal fed from the output resonator 4 to the adder 6, by the use ofthe phase shifter 5, and varying the coupling with the output resonator4 so that the amplitude of the signal in the adder 6 fed from the outputresonator 4 is equal to the amplitude of the signal applied from theintermediate resonator 3, while the phases of said signals are opposite.The amplitude and phase selection is correct if the indicator 9 readszero level of the r-f signal in the adder 6.

After the amplitudes and phases of the signals tapped from the outputand intermediate resonators 4 and 3 have been selected, the sum signalfrom the adder 6 is fed to the input resonator 2 of the klystron 1. Thenext step is to vary the anode voltage. Changing the phase of thesignals from the output and intermediate resonators 4 and 3 of theklystron 1 will cause the sum signal in the adder 6 to differ from zeroand an additional adjusting signal will appear at the input resonator 2.Changing the phase of the adjusting signal at the input resonator 2 ofthe klystron 1 with the additional phase shifter 7 so that the phaseshift change in the klystron 1 due to the anode voltage variation is setto a minimum, it will be possible to provide optimum adjustment ofphase-shift instability and restore the nominal operating voltage.

The following symbols are used on the vector diagrams of FIGS. 2 and 3illustrating the preferred embodiment of the invention:

U₁ =r-f voltage at the output resonator 4 of the klystron 1;

U₂ =r-f voltage at the intermediate resonator 3 of the klystron 1;

U₃ =r-f voltage at the input resonator 2 of the klystron 1;

U₄ =r-f voltage at the input resonator 2 of the klystron 1 withoutfeedback furnished by an input power source;

U₅ =adjusting r-f signal fed from the adder 6 to the input resonator 2with anode voltage variations; and

k and t=coefficients of transmission of r-f voltages from the output andintermediate resonators 4 and 3 to the input resonator 2 of the klystron1 with account for phase delays in the transmission line.

With the above configuration of the device for adjusting a phase shift,under nominal operating conditions (FIG. 2) when kU₁ =-tU₂, theadjusting signal U₅ =O and the r-f voltage at the input resonator 2(FIG. 1) of the klystron 1 will be determined solely by the input powersource U₃ =U₄ (FIG. 2) and the mu factor of the klystron 1 (FIG. 1) willbe equal to the mu factor of the klystron 1 without feedback.

In the event of any variation resulting in a change of the phase of theoutput signal by an angle β (FIG. 3), the phase of the signal in theintermediate resonator 3 (FIG. 1) will change by a value α (FIG. 3)since the distance from the input resonator 2 to the intermediateresonator 3 (FIG. 1) is smaller than the distance from said intermediateresonator to the output resonator 4. Actually, a phase shift φ (FIG. 3)of the r-f voltages at the resonators 2, 3, and 4 (FIG. 1) arrangedalong the klystron 1 is determined by the following relationship:##EQU1## wheref=operating frequency;

l=distance from the input resonator 2;

m/e=ratio of charge to electron mass;

U_(o) =anode voltage of the klystron 1.

From the equation (1) it follows that a greater distance corresponds toa larger phase shift as the anode voltage of the klystron 1 is varied.Referring to the vector diagram of FIG. 3 illustrating operation of theklystron 1 under the conditions differing from the rated mode it is seenthat kU₁ ≠-tU₂ and the input resonator 2 (FIG. 1) of the klystron 1accepts the adjusting voltage signal U₅ from the adder 6. In this case,U₃ ≠U₄ (FIG. 3) and the signal voltage at the input resonator 2 (FIG. 1)of the klystron is phase-shifted with respect to the voltage of theinput power source through an angle ξ (FIG. 3) in the direction oppositeto that of the input signal phase variation. The phase of the outputsignal will, thus, be adjusted. With a sufficiently high level of thetapped signals it is possible to obtain such an adjusting voltage U₅,that ξ=β and the phase shift instability is fully compensated.

Inasmuch as the phase of the adjusting voltage is shifted through 90°with respect to the voltage at the input resonator 2 (FIG. 1), the valueof said voltage will change but slightly with varying anode voltage ofthe klystron 1. The mu factor of the klystron 1 will also be unchanged.

The use of a cavity resonator or a narrowband filter prevents spuriousoscillations from occurring at unwanted frequencies.

The method according to the invention makes the requirements for powersource stability less stringent, an advantage decreasing, in its turn,dimensions, weight and cost of power sources of the klystron 1.

Industrial Use

The invention may be used in radio equipment wherein the phase ofamplified signals should have increased stability, say, in transmittersof radar sets incorporating an MTI circuit, high-power charged-particleaccelerators supplied with r-f signals, and in other devices, in which amulticavity klystron is used as an r-f energy source.

We claim:
 1. A method of adjusting a phase shift in an amplificationmulticavity klystron including an input resonator, an intermediateresonator and an output resonator, said method comprising the stepsof:tapping a portion of a signal from the output resonator; tapping aportion of a signal from the intermediate resonator; adding the signalstapped from the output and intermediate resonators to obtain a sumsignal; applying the sum signal to the input resonator of the klystron;and adjusting amplitudes and phases of the tapped signals so that thetapped signals have equal amplitudes but opposite phases; wherein anodevoltage is varied until the phase shift in the klystron changes, andcomprising the subsequent step of selecting the phase of the sum signalso as to provide a minimum phase-shift variation in the klystron.
 2. Adevice for adjusting a phase shift in an amplification klystron,comprising an input resonator, an intermediate resonator, an outputresonator, and means for transmitting a signal from the output resonatorto the input resonator of said klystron, said means for transmittingcomprising a phase shifter, a signal adder coupled to the phase shifter,the intermediate resonator and the output resonator, and an additionalphase shifter inserted between the adder and the input resonator toprovide for selection of the phase of an adjusting signal.